Evolution Unit:

Okapi Evolution

Hominid Evolution

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Agenda Spring 2001

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Stripes of the Okapi

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The Okapi is a medium sized relative of the giraffe, which lives in isolated parts of the jungles of the Zaire. First discovered in 1885, zoologists have recorded the information in Table A & B regarding the stripe pattern on the Okapis' rear. They either have a plain rear, striped, or a densely striped "white" appearance. During this time, no predators of the Okapi had been identified and the population appeared to be stable. In 1923, leopards were spotted in this region for the first time and were found to be feeding on Okapis. Studies of leopards preying on Okapis showed that they had the greatest success capturing Okapis with plain rears, or with a large number of stripes (thus making the rear appear almost all white). Table B shows statistics on Okapi stripes after many years of leopard predation. Corresponding genotypes are included from genetic studies. Note that stripes tends to be a co-dominant trait.

Table A Table B

# of 0kapi
# of Okapi
Plain (PP)
Plain (PP)
Striped (Pp)
Striped (Pp)
"white'' (pp)
"white" (pp)


  1. Describe the change in the Okapi population since their discover in the 1800's.
  2. Three forms of Natural selection occur; dependent upon the direction of the character change. Which is the above an example of?
  3. What trait or characteristic is being selected for in this example?
  4. What is the selective force within the environment?
  5. The "Giraffe" family originated in the plains of Africa, then moved into the forest. Explain how the neck length may have shortened in the Okapi population?

Fill in the following table:

Total # of alleles in both A & B


Total # of alleles in both A & B


# of P alleles in A


# of P alleles in B


# of p alleles in A


# of p alleles in B


Gene Freq. (%) for P in example A


Gene Freq. (%) for P in example


Gene Freq. for p in example A


Gone Freq. for p in example B